17 research outputs found
Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
We present a high-resolution microwave spectrometer to measure the
frequency-dependent complex conductivity of a superconducting thin film near
the critical temperature. The instrument is based on a broadband measurement of
the complex reflection coefficient, , of a coaxial transmission
line, which is terminated to a thin film sample with the electrodes in a
Corbino disk shape. In the vicinity of the critical temperature, the standard
calibration technique using three known standards fails to extract the strong
frequency dependence of the complex conductivity induced by the superconducting
fluctuations. This is because a small unexpected difference between the phase
parts of for a short and load standards gives rise to a large
error in the detailed frequency dependence of the complex conductivity near the
superconducting transition. We demonstrate that a new calibration procedure
using the normal-state conductivity of a sample as a load standard resolves
this difficulty. The high quality performance of this spectrometer, which
covers the frequency range between 0.1 GHz and 10 GHz, the temperature range
down to 10 K, and the magnetic field range up to 1 T, is illustrated by the
experimental results on several thin films of both conventional and high
temperature superconductors.Comment: 13 pages, 14 figure
Dynamic fluctuations in the superconductivity of NbN films from microwave conductivity measurements
We have measured the frequency and temperature dependences of complex ac
conductivity, \sigma(\omega)=\sigma_1(\omega)-i\sigma_2(\omega), of NbN films
in zero magnetic field between 0.1 to 10 GHz using a microwave broadband
technique. In the vicinity of superconducting critical temperature, Tc, both
\sigma_1(\omega) and \sigma_2(\omega) showed a rapid increase in the low
frequency limit owing to the fluctuation effect of superconductivity. For the
films thinner than 300 nm, frequency and temperature dependences of fluctuation
conductivity, \sigma(\omega,T), were successfully scaled onto one scaling
function, which was consistent with the Aslamazov and Larkin model for two
dimensional (2D) cases. For thicker films, \sigma(\omega,T) data could not be
scaled, but indicated that the dimensional crossover from three dimensions (3D)
to 2D occurred as the temperature approached Tc from above. This provides a
good reference of ac fluctuation conductivity for more exotic superconductors
of current interest.Comment: 8 pages, 7 Figures, 1 Table, Accepted for publication in PR
Contact inspection and resistance–capacitance measurement of Si nanowire with SEM voltage contrast
A Stem Cell Harvesting Manipulator with Flexible Drilling Unit for Bone Marrow Transplantation
Abstract. We present the development of an innovative device (Stem Cell Harvesting Manipulator) to get a donor’s hematopoietic stem cells for bone marrow transplantation with minimal puncture. In this paper, we report the development of a prototype of the manipulator with Flexible Drilling Unit. The manipulator is inserted into the medullary space from the iliac crest and aspirates the cells while an end-mill on the tip of the Flexible Drilling Unit drills through cancellous bone to create a curved path. We found that the manipulator could be inserted into the pig iliac bone 131 mm by 32.1 mm/min. Moreover, the number of harvested nucleated cells per puncture is 6.04 times more than the Aspiration Method. The Aspiration Method, however, could harvest much (3.73 times) denser graft than our method. Further consideration regarding whether or not this device can harvest viable hematopoietic stem cells should be considere